1. Field of the Invention
The present invention relates to a solid catalyst component for .alpha.-olefin polymerization. More specifically, the present invention relates to a solid catalyst component for .alpha.-olefin polymerization having a narrow particle size distribution and high catalytic activity, a catalyst for .alpha.-olefin polymerization comprising said solid catalyst component and a process for producing poly-.alpha.-olefins with said catalyst.
2. Description of the Related Arts
As is well known, the ziegler-Natta catalyst comprising a transition metal compound (IV to VI Groups) and an organometallic compound (I, II and XIII Groups) is used for producing isotactic polymers of an .alpha.-olefin such as propylene, 1-butene or the like.
For the improved operability, it is desirable to produce poly-.alpha.-olefins having a substantially uniform particle diameter and being free from fine powder. Catalyst residues deriving from the transition metal compound and the organometallic compound remain in the resulting poly-.alpha.-olefins. An equipment for removal of the catalyst residue is required for removal and deactivation of the catalyst residue, which arises various adverse effects on the stability and processability of poly-.alpha.-olefins, and the like.
the problem of the catalyst residue is solved by increasing the catalytic activity, which is defined as the weight of the produced poly-.alpha.-olefin per unit weight of the catalyst. This method does not require any special equipment for removal of the catalyst residue, and reduces the production cost of poly-.alpha.-olefins. The catalyst having extremely high catalytic activity is required to enable a deashing-free process that is industrially advantageous.
The higher catalytic activity, however, decreases the bulk density of the resulting polymer particles. Therefore, a catalyst having a high activity and giving polymers of high bulk density and favorably particle properties, is required. Development of the solid catalyst component having the favorable particle properties and high polymerization activity has been attempted because the particle properties of the resulting polymers significantly depend upon the particle properties of the solid catalyst component.
With respect to an improvement the particle properties and narrowing the distribution of particle size, in polymerization of ethylene, there are proposed uses of a solid catalyst component preparing by supporting a titanium-magnesium compound on a silica gel carrier to overcome the problems (JP-A-148093 and JP-A-56-47407). It is also disclosed in JP-A-62-256802 that, in polymerization of propylene, particle properties of the resulting polypropylene are markedly improved by using the solid catalyst component obtained by soaking a titanium-magnesium compound in silica gel as a carrier.
Although improving the particle properties to some extent, these proposed catalysts have relatively low activity and cause a large amount of silica gel used as the carrier to contaminate in the final products. The contaminated silica gel deteriorates the quality of final products and causes fish eye in film products.
A variety of solid catalyst components having a high catalytic activity have also been proposed.
By way of example, it is known that a Ti-Mg complex-type solid catalyst, which is obtained by reducing a tetravalent titanium compound with an organomagnesium compound in the presence of an organosilicon compound to obtain an eutectic crystal of magnesium and titanium, is used in combination with an organoaluminum compound as a co-catalyst and an organosilicon compound as a third component to realize .alpha.-olefin polymerization of relatively high stereoregularity and high activity (JP-B-03-43283) and JP-A-01-319508). Another proposed technique shows that coexistence of an ester in the reduction of a tetravalent titanium compound with an organomagnesium compound in the presence of an organosilicon compound further improves polymerization of higher stereoregularity and higher activity (JP-A-216017).
Although these proposed techniques realize an extraction-free and deashing-free process, further improvement in particle properties of the resulting polymers is desired.